1. Field of the Invention
The present invention relates to a method and an apparatus for predicting an intake manifold pressure of an internal-combustion engine. In particular, the present invention relates to a method and a fuzzy estimator for predicting an intake manifold pressure, using fuzzy algorithm.
2. Description of the Related Art
Fuel injection control is carried out for efficient combustion in internal-combustion engines. FIG. 1 shows an intake portion of an internal-combustion engine, to which the present invention is applied. A drawn air is supplied to a cylinder through a throttle 1. Throttle opening is controlled at a desired value. An intake manifold pressure is measured with a sensor 2. For appropriate fuel injection control, an amount of air to be drawn into the cylinder must be estimated and therefore a value of intake manifold pressure must be predicted.
Conventionally, such an intake manifold pressure predicting apparatus as described below was disclosed, for example in Publication of Japanese Unexamined Patent Publication (KOKAI) No. 2-42160. The apparatus predicts an intake manifold pressure at the present time based on operating states of the internal-combustion engine and predicts intake manifold pressure at a time of prediction, a certain period ahead, based on the predicted intake manifold pressure and a detected value of intake manifold pressure.
However, the above-mentioned predicting apparatus was not able to make a prediction with sufficient accuracy over a wide range of number of revolutions of the internal-combustion engine. The reason is that the apparatus corrects a predicted intake manifold pressure during a period while an intake valve is transiently closed, evenly based on an error in intake manifold pressure ΔP and independently of operating states of the internal-combustion engine.
Japanese Patent No. 2886771 discloses an intake manifold pressure predicting apparatus which makes a prediction considering operating states of the internal-combustion engine to solve the above-mentioned problem, and enables a high accuracy control even in the case of lower number of revolutions and higher intake manifold pressures.
In the conventional method mentioned above, a predicted value of intake manifold pressure (hereinafter referred to as HATPB) is calculated based on a difference (hereinafter referred to as ΔPB) between successive values of intake manifold pressure (hereinafter referred to as PB) and a difference (hereinafter referred to as ΔTH) between successive values of throttle opening. Further, HATPB is used for fuel injection control and retrieval of parameters for fuel adhesion correction. Now, ΔTH and ΔPB are represented as below provided that k is a point in control time synchronized with intake stroke (TDC).ΔTH(k)=TH(k)+TH(k−1)  (1)ΔPB(k)=PB(k)+PB(k−1)  (2)
On the other hand, between the detecting portion of a PB sensor and an intake manifold, on the intake manifold side or in the PB sensor, a labyrinth mechanism or the like has recently been provided to prevent water from entering there. Accordingly, a time lag and a time delay between an actual value of pressure and an output of the PB sensor, have become larger.
There have been attempts to use conventional prediction algorithms to compensate the time delay. However, the algorithms have caused an overshoot of HATPB against an actual PB, as shown in FIG. 2 or a discontinuous behavior of HATPB. The reason for the overshoot is that the conventional prediction algorithms make up for insufficient accuracy of a predicted value of PB through feedback of an error between a predicted value of PB a certain time in advance and the current value of PB. Further, the reason for the discontinuous behavior is that the conventional prediction algorithms use one of predicted values calculated respectively based on ΔPB and ΔTH, by switching according to certain conditions. Such behaviors of the conventional prediction algorithms have such an influence on fuel injection control as to cause a problem that variation in variables during transient operations becomes larger to increase an amount of emissions of offensive exhaust elements.
Accordingly, there has been a need for a new prediction algorithm for PB to compensate for a larger lag and a larger time delay without producing an overshoot or a discontinuous behavior of HATPB.